When the misfits of Class 3-E get stuck with a smiley-faced, octopus-tentacled schoolteacher with bizarre superpowers, they discover they have a lot to learn...

Koro Sensei has already blown up the moon. He promises not to do the same to the Earth on one condition...that he be allowed to teach a certain junior high school remedial class for one year. In addition, he'll allow the students to attempt to take him out at any time without retaliating. Whoever succeeds gets a huge cash reward from the Ministry of Defense. But now the students of Class 3-E are the only ones standing in the way of the destruction of the planet!

Meet the would-be assassins of class 3-E: Sugino, who let his grades slip and got kicked off the baseball team. Karma, who's doing well in his classes but keeps getting suspended for fighting. And Okuda, who lacks both academic and social skills, yet excels at one subject: chemistry. Who has the best chance of winning that reward? Will the deed be accomplished through pity, brute force or poison...? And what chance does their teacher have of repairing his students' tattered self-esteem?